A video of two children smoking cigarettes on a train has sparked fresh debate about the scale of China’s tobacco habit.The short video shows two young boys - aged approximately three to four years old - laughing as they puff away, with one blowing smoke into the others face.When one surprised passenger asks ‘Does he know how to smoke?’, another replies, ‘Yes, you see he can inhale!’, according to the website behindthewall.com.The young pair are stood on the space between two connecting train carriages, which often serves as a smoking area on Chinese trains. Smoking is a huge problem in China. The cost per year to the health service was more than 70billion yuan last year - approximately £6.5bn.It has arguably the biggest smoking problem in the world, with at least one million deaths per year from smoking related illnesses. As much as 30% of China’s population smokes - around 300 million people - compared to around 10 million adults in Britain. As many as 53 per cent of adult men smoke in China.Smoking was banned in public places in Britain came into force on July 1, 2007, and smoking rates have been steadily dropping for decades. China first mooted a ban as far back as 1995 and while any such plans have been fiercely opposed, restrictions are extended regularly.The latest initiative, announced last month, will ban smoking starting May 1 in all indoor public areas.